(1) Field of the Invention
The present invention relates generally to a system and method for detecting and determining the occurrence of a knocking in an internal combustion engine with a high accuracy thereof maintained against aging effects.
(2) Background of the art
A Japanese Patent Application First Publication (Non-Examined) Sho 53-60430 published on May 31, 1978 exemplifies a conventional knocking determining and controlling system.
In the above-identified Japanese Patent Application Publication, a knocking sensor is installed on a cylinder block (or cylinder head) of an internal combustion engine A knocking vibration detecting portion of a knocking control unit filters the output signal from the knocking sensor so as to extract a frequency component particular to the knocking occurrence (for example, several KHz). The intensity of the frequency component is determined by means of a knocking intensity determining portion. If the intensity exceeds a predetermined level, the knocking control unit deems that the knocking has occurred and a retard angle controlling portion retards the ignition timing so as to suppress the knocking.
Furthermore, a Japanese Utility Model Application Publication sho 60-80335 published on June 4, 1985 exemplifies another knocking determining and controlling system. In the Japanese Utility Model Application Publication, the output level of an integrator for integrating a particular detected and amplified frequency component of vibration in a combustion chamber of an engine cylinder is adjusted according to the engine revolution speed so as to accurately detect the occurrence of knocking.
However, in the conventional knocking controlling method, the so-called "Q" of the vibration generated by the knocking is small, "Q" being the width of the particular frequency, and when "Q" is large, the particular frequency is more clearly defined. In addition, in the conventional knocking controlling method, mechanical noise (background noise) of the engine in the detected signal of the knocking sensor cannot perfectly be eliminated. Therefore, this knocking determining method is not always accurate. Consequently, unnecessary retardation angle controls are carried out because of background noise occurring at the particular frequency peculiar to the knocking, especially when the engine revolves at a high speed in which the mechanical noises are increased.
While more accurate knocking detecting means are available, they are complex and heavy and their cost is prohibitively high and, furthermore, the detection accuracy of knocking reduces with age.